In computer graphics, various graphical shapes are created and rendered by the employment of basic graphical building blocks, known as graphics primitives. One widely-used graphics primitive is a triangle graphic primitive. Triangle primitives can be aggregated into triangle strips. The triangle strips comprise a row of triangle primitives aggregated together in alternating apex-orientations, both upwards and downwards. Triangle strips are typically a flexible unit of computer graphic manipulation because they can represent a single triangle (that is, a “three vertex” triangle strip), a single quadrilateral (that is, a “four vertex” triangle strip), or a rectangular lattice comprising a plurality of vertically-aggregated triangle strips. A rectangular lattice is generally defined as a rectangular two-dimensional aggregation of a plurality of rows of triangle strips, wherein internal vertices are repeated during transmission.
Employing triangle strips can be reasonably data efficient for the transmittal and rendering of long aggregations of triangle primitives to create a single row. This is because, in a triangle strip, the number of vertices per graphical triangle shaped primitive approaches the ratio of one to one, thereby necessitating the transmission of a minimum number of vertices to render (that is, to graphically recreate and display) a triangular strip.
However, the employment of triangle strips to render a rectangular lattice entails inefficiencies. Generally, the inefficiencies are because each row of vertices internal to the rectangular lattice has to be repeated. For instance, a rectangular lattice, comprising 24 equilateral triangles, actually requires 30 strip vertices to be rendered (eight triangles per row by three rows).
Subdivision surfaces, that is, the graphical technique of segmenting a given shape into constituent sub-shapes, are becoming ever more widely employed in graphics. However, subdivision can be especially inefficient with respect to data transfer overhead, particularly when triangle strip data is generated. This is typically because, similar to a rectangular lattice, internal row vertices are repeated. In the limit (that is, as the subdivision level approaches infinity), the efficiency approaches 50%.
A second approach to graphical design is to directly support basic graphical primitives so that internal row vertices need not be repeated. This creates a mesh, such as a rectangular mesh. A rectangular mesh is generally defined as a rectangular aggregation of graphics primitives, wherein the rectangular aggregation of graphics primitives did not occur due to the two-dimensional aggregation of a plurality of triangle strips.
In one known approach of creating a rectangular mesh, the renderer caches both the previous row of vertices of a given row of aggregated triangle-shaped or quadrilateral-shaped primitives. Then, instead of receiving both rows of vertices for the next row of aggregated triangle-shaped or quadrilateral-shaped primitives, the renderer only receives the top row of vertices for the next row of aggregated triangle-shaped or quadrilateral-shaped primitives, thereby reducing the transmitted information needed to draw the rectangular mesh and increasing efficiency. Rendering a rectangular mesh can be more efficient than rendering a rectangular lattice created by the aggregation of primitive strips.
However, processor performance has outpaced memory and bus performance, while at he same time, the employment of subdivision surfaces has increased the demand for higher throughput. Therefore, there is a need for employing graphics primitives for rendering a subdivided triangle that overcomes the shortcomings of existing approaches.